The invention relates to removing coatings from a surface and more particularly to removing paint, varnish or biological growth from the outer hull of a boat.
The removal of a layer or layers from a surface by impacting an abrasive material against the layer or layers is well known. For example, grit or sand-blasting has been used for many years to clean stone buildings, painted metal surfaces such as railings and superstructures including oil rigs. The particles of grit or sand are mobilised by means of a carrier fluid, normally air or water.
The commonly used methods suffer from the drawback that damage is often caused to the material beneath those layers being removed. This is especially true where the methods are employed to remove surfaces from a relatively soft material such as wood or fibre glass. In particular, where fibre glass is being cleared, damage can be caused to the gel coat layer. The problem of damage caused is particularly acute where, for example, antique wooden objects are being cleaned or where the surface is part of a boat.
German patent application DE 195222001 (MINERALIEN WERKE) discloses the use of a mixture of solids, on of the solids having a higher density than the other, in order to clean and treat sensitive or polished surfaces such as brick or marble.
Where water is used as the carrier fluid, then its consumption using conventional methods is often quite high. Where there is a ready supply of water high consumption may not be a problem but where, due to the remoteness of a source, the water needs to be transported to the object to be cleaned, minimisation of water consumption would be advantageous.
It is an object of the present invention to provide a method which alleviates the above disadvantages. It is a further object of the present invention to minimize the usage of the carrier fluid when said fluid is a liquid.
In accordance with the invention there is provided a method of removing a coating such as paint or varnish from a surface, the method comprising:
(i) selecting a particulate solid suitable for removing the coating from the surface, the particulate solid having a particle size from 150 to 250 xcexcm;
(ii) selecting a fluid as a carrier for the particulate solid;
(iii) distributing the particulate solid in the fluid to form a spray mixture;
(iv) generating a presurised jet of the spray mixture;
(v) impacting onto a coating, the pressurised jet of spray mixture to remove the coating.
Preferably, the particle size is from 170 to 190 xcexcm.
The hardness of the particulate solid is preferably less than 8.0 on the Moh scale. It is particularly preferable for the hardness to be 6.0 to 7.0 on the Moh scale. The preferred particulate solid is olivine.
In one arrangement, the method includes heating the carrier fluid.
The fluid is preferably a liquid. It is particularly preferable that the liquid used is water.
The temperature of the liquid is preferably maintained below 50C. It is particularly preferable that the liquid is heated to a temperature between 25 and 40C.
The solid to liquid ratio in the jet spray is preferably approximately 2 to 1 volume for volume.
The jet advantageously is directed to impact the coating at an angle of approximately 45xc2x0.
In use, the jet is movedxe2x80x94preferably in a circular motionxe2x80x94back and forth across the coating to be removed.
The pressure of the jet is advantageously from 3x105 to 1.5x106 Nmxe2x88x922 and preferably from 4x105 to 1x106 Nmxe2x88x922.